Mobihel > Coating defects
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The causes and elimination of coating defects


At the everday's use of coatings, sometimes the defects occur, which are not always due to worse coating quality, but often linked to not knowing the materials enough, their correct use, application conditions and application technique. It is very important, that we know to analyze such defects, establish the cause and most important prevent it.
This manual will help you to achieve this. We tried to present as clearly as possible the most frequent coating defects, which occur, to define the causes and above all to give instructions for their prevention.
We wish you a lot of success!

PUTTYING
PAINTING PRIMERS
TWO AND THREE-LAYER PAINTING

Reasons for, and prevention of defects when puttying

Poor Drying  
Reasons:
  • added too small quantity of hardener
  • high air humidity, which increase drying time,and also causes clogging of the paper
  • material gets reduced
     
Repair of the incurred defect:
  • sand back to bare metal and repeat puttying according to instructions
Spots or bleaching in the top coat  
Reasons:
  • too much hardener in PE putty
  • badly mixed in hardener in PE putty
     
Prevention:
  • check addition of a hardner
  • mix thoroughly
     
Repair of the incurred defect:
  • sand back to bare metal and repeat puttying according to instructions
Pin Holes  

 

Reasons:
  • incorrect puttying (presence of air or thick coats)
  • surface is not dried through enough
  • too thin primer coat
     
Prevention:
  • with a spreader you should press down on the mixing board in the same place several times in order to force out the air
  • dont putty in high thicknesses, you should apply several thin coats
  • sand the pin holes or apply putty to them
  • always isolate PE putty prior to application of a top coat
     
Repair of the incurred defect:
  • sand to bare metal and repeat puttying according to instructions
Traces of sanding marks  
Reasons:
  • sanding of putty with unsuitable (too coarse) abrasive paper
  • sanding of old lacquering with unsuitable (too coarse) abrasive paper
     
Prevention:
  • use abrasive paper of the prescribed grit- sand rough cracks with a fine abrasive paper
     
Repair of the incurred defect:
  • sand to bare metal and repeat puttying
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Causes and prevention of defects when painting primers

Blisters  

 

Causes:
  • too short flash off times between coats
  • too thick primer coats
  • water residue from sanding in corners, edges, folders and under decorative borders
  • water hardness for sanding is too high
  • polluted compressed air
  • too high air humidity (over 80 % at 2K materials)
  • condensed water due to temperature fluctuations
     
Prevention:
  • Flash off between coats min. 10 min./20°C
  • Maximum application 80µm at HS filler and max. 40µm at MS filler
  • if possible, always dismantle component parts
  • blow off carefully
  • do not allow water residue from sanding to dry, they should be wiped clean
  • compressed air should be dry and clean
  • avoid the formation of condensed water, keep a stable temperature and humidity
     
Repair of incurred defect:
  • sand to bare metal and repeat painting of a primer according to instructions
Traces of sanding in a top coat
 

 

Causes:
  • sanding of the primer with unsuitable (too rough) abrasive paper
  • sanding with unsuitable (too rough) abrasive paper on old lacquering
  • insufficient putty isolation prior to application of top coat
  • too low viscosity of top coat
     
Prevention:
  • use abrasive paper of prescribed grit
  • sand rough cracks with a fine abrasive paper
  • isolate thoroughly puttied repairs with a filler
  • follow the prescribed viscosities of top coats
     
Repair of incurred defect:
  • sand to bare metal and repeat painting of a primer according to instructions
Bad adhesion to surface  

 

Causes:
  • badly prepared surface, grease traces,finger prints, powder, dust etc
  • use of materials, which are not suitable for certain types of metals
  • thinning of material with unsuitable (not original) thinner
     
Prevention:
  • clean surface thoroughly before painting
  • always check, which material can be applied to a certain type of metal
  • use of recommended thinners
     
Repair of the incurred defect:
  • sand to sheet metal and repeat painting of a fillerr according to instructions
  • take care to use the correct 2K primer /filler with regard to surface
Soaking of a surface  
Causes:
  • not dried through, not cured old enamel
  • too high coat thickness of old enamel
     
Prevention:
  • follow the prescribed drying times
  • follow the prescribed coating thickness
     
Repair of the incurred defect:
  • sand to bare metal and repeat painting of a primer according to instructions
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Reasons and prevention of defects with two and three-layer painting

 Cloudiness  
 

 

Reasons:
  • unsuitable application technique (nozzle, pressure)
  • too short flash off times
  • use of unsuitable thinner
  • the suface, which we paint has no adequate temperature (too cold or too warm)
     
Prevention:
  • use of the prescribed application technique
  • use of a prescribed thinner
  • assure a suitable surface and room temperature ( 18 - 20˚C), where we paint, and max. humidity 40 – 60%
     
Repair of the incurred defect:
  • sand to the primer and repeat painting of base enamel according to instructions
 Deviation of colour shades  

 

Reasons:
  • not following the prescribed conditions for application (nozzle, pressure, distance of a gun)
  • incorrect spraying technique : too wet, too dry, not covering
  • surface damaged due to weather influences and use of unsuitable cleaners
  • deviation of the painting process
  • using a badly mixed colour shade
     
Prevention:
  • following the prescribed application conditions
  • spraying “fade out” technique
  • tinting at partial painting
  • prior to use mix colour shade thoroughly
     
Repair of the incurred defect:
  • sand to the primer and then repeat the painting process according to instructions
 Craters  
  Causes:
  • wax, grease, silicone residue
  • compressed air contaminated through condensed air or oil residue
  • use of silicone, polishing agents or sprays
  • the surface was not sufficiently cleaned before coating
     
Prevention:
  • before coating clean the surface thoroughly with
  • MOBIHEL Antisilicone cleaner low VOC or MOBIHEL HYDRO Cleaner
  • regular maintenance of oil and water separators (filters)
     
Repair of the incurred defect:
  • sand the surface to a primer and repeat painting of the top coat according to the recommendations
 Sagging  
 

 

Causes:
  • Incorrect viscosity of HYDRO Base
  • too high film thickness of HYDRO Base
  • unsuitable spray gun (nozzle), pressure
  • too cold material, substrate or too low room temperature
  • use of unsuitable thinner
     
Prevention:
  • follow technical instructions for use
  • use a suitable spraygun
  • warm the object and material to room temperature + 20°C
  • use a recommended thinner
     
Repair of the incurred defect:
  • sand to the filler and repeat painting of Base according to instructions
Matt effect (gloss decrease)  
 

 

Causes:
  • too high coat thickness MOBIHEL 2K HS 2:1 clearcoat low VOC (more than 2 coats)
  • too high air humidity
  • surface soaking
  • hardener defects – hardener reacted with air humidity
  • humidity in compressed air supply
     
Prevention:
  • follow technical instructions for the application of material
  • keep hardener cans sealed properly
  • enable sufficient air flow (during drying)
  • follow drying times
  • use the recommended hardener
     
Repair of the incurred defect:
  • sand to the primer and repeat the application of MOBIHEL 2K HS 2:1 clearcoat low VOC according to regulations
  • check quality of a hardener – it should be clear, colourless, fluently running, without any floating particles.
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